The rapid development of the modern telecommunications carrier network has been driven by the ever-increasing demand for computer-based voice, video and data services, and as a result, there is an increased demand for larger bandwidth channels over extended distances, to handle the high-speed digital bandwidth applications. The existing telecommunications network contains carriers at specific rates that may not match the needed bandwidth of the user. These carriers were originally designed to handle voice calls which have been digitized at a 64 Kbs rate, and contain a hierarchy of multiplexing so as to carry multiple voice calls on a single carrier.
In the International Telecommunications Union (ITU) G.704 system used in Europe, there exists a first level multiplex rate of 2.048 Mbps, commonly referred to as an E-1 signal, which can carry 32 channels of 64 Kbs each, which typically represent 30-31 voice channels and one control channel. However, the E-1 signal can also be used to carry a “clear” signal of 2.048 Mbps, which is not divided into 32 channels. Higher level multiplexing is done in stages, with an E-2 signal containing 4 multiplexed E-1 signals at a bit rate of 8.448 Mbps, and an E-3 signal containing 4 multiplexed E-2 signals at a bit rate of 34.368 Mbps. At each stage of multiplexing, a certain amount of overhead is required, and therefore the bit rate is slightly higher than the sum of the individual multiplexed signals.
In North America, the ANSI standard T1.107 has an equivalent multiplexing hierarchy, with a T-1 or DS-1 signal representing 24 multiplexed voice channels at a 1.544 Mbps bit rate, a DS-2 signal containing 4 DS-1 signals at a 6.312 Mbps bit rate, and a DS-3 signal containing 7 DS-2 signals at a 44.736 Mbps bit rate. The higher order signals may also be used to carry “clear” signals which do not consist of multiplexed channels, but are instead utilized as simple data carriers at the above mentioned bit rates.
It is often necessary to carry data rate signals originating in one system, e.g. the ITU system, by a North American carrier signal. Thus, a clear E-3 signal, containing a data rate 34.368 Mbps may be carried on a DS-3 carrier which has a bit rate of 44.736 Mbps.
In addition to the above signals, two synchronous systems originally designed for optical transmission exist, namely SONET (Synchronous Optical Network) utilized primarily in North America, and SDH (Synchronous Digital Hierarchy). Both of these standards are designed to handle clear signals at their originating rate for ultimate transport over the network. Thus, an SDH network operating at 622.08 Mbps signals, may carry a large number of 2.048 Mbps signals originating as E-1 signals, and may also carry E-3 and DS-3 signals. This is done in virtual containers, as described in ITU-T recommendation G.707 for SDH systems and in ANSI standard T1.105 for SONET systems.
As mentioned above, however, these carriers exist at a specific data rate, which may not match the bandwidth required by the user. This problem is addressed by the inverse multiplexing technique which enables low bandwidth communications channels to be combined into a single, high bandwidth communication channel.
An example of a system addressing the mismatch of existing telecommunication network bandwidths with the high data rate applications exceeding the available bandwidths, is disclosed in U.S. Pat. No. 5,065,396 to Castellano. An inverse multiplexing technique is disclosed for use in demultiplexing a high data rate input signal into lower rate subsectional or sub-stream output signals, which are then transmitted over existing lower rate transmission facilities. At the receiving end, the lower rate sub-stream signals are recovered and provided as inputs to a resynchronizing means, for producing the original signal and transmitting it to an end user device.
In U.S. Pat. No. 5,251,216 to Mann et al, there is disclosed a method of transforming multiple low bandwidth telecommunication channels into a single high bandwidth telecommunication channel. This is achieved by disassembly of a large datastream on a high bandwidth channel into multiple datastreams for transmission on low bandwidth channels, and the re-assembly of the individual datastreams on the low bandwidth channels into a single aggregate datastream on a high bandwidth channel. The disassembly occurs with the transmission of data, and the re-assembly occurs on receiving the data.
The Mann patent refers to a problem relating to the standard channels which have a bandwidth which does not match the required data rate bandwidth. Available North American channel capacity, such as in the case of a common T1 signal is 1.544 Mbps, whereas the next commonly available bandwidth step in the hierarchy is a T3 signal having a data rate of 44.736 Mbps. When an intermediate capacity is required, the typical solution is to use several individual T1 signals or use an entire T3 signal in which only a portion of the available bandwidth capacity is used, thus wasting available bandwidth capacity.
In cases, where a “clear” E-3 signal is used, there are no individual E-1 signals to be recovered. The entire “clear” E-3 signal may be transferred within the DS3 signal, but since the E-3 signal has a 34.368 Mbps and the DS3 signal has a bandwidth of 44.736 Mbps, the extra bandwidth capacity is wasted.
Prior art solutions attempt to meet the mismatch between available carriers, and the desired data bandwidth channels by using the inverse multiplexing technique to aggregate low bandwidth channels to provide a larger bandwidth. This is clearly not economical in the above example, where 23 DS-1 signals would be needed, each at a rate of 1.544 Mbps to carry the clear E-3 signal. Thus a method to efficiently utilize the bandwidth when carrying a clear data signal in a higher speed channel is needed.